Brominated perfluorocarbon compounds are of particular interest in medical science because of their high degree of thermal and chemical stability and because of their unusual resistance to chemical attack by most reagents. Of particular importance is their extremely low toxicity and inertness when introduced into the tracheobronchial tree and lungs. Preliminary studies in this laboratory have demonstrated that emulsion preparations provide excellent visualization of the tracheobronchial tree in laboratory animals. Pure liquid preparations possess the property of outlining the alveolar structures without overlying visualization of the bronchial structures. These radiopaque flurocarbons are also useful in x-ray visualization of the gastrointestinal tract, spleen, urinary bladder and blood vessels. Additional studies will be performed to evaluate the effects of brominated perfluorocarbons on airway mechanics, gas exchange and mucociliary clearance and on the structure of the tracheobronchial tree and alveoli of experimental animals. The goals of the research are to provide a new and safe contrast medium for use in studies of pulmonary diseas in humans. In subsequent years of support, broad application will be attempted by using this radiopaque material for visualization of such structures as the G.I. tract, blood and lymphatic vessels, spleen, hollow structures of the central nervous system, the biliary system, pancreatic ducts, and the lower urinary tract.